(KFSN) Fresno, Calif., Police Chief Jerry Dyer discusses the arrest of a 15-year-old girl who threatened a school shooting on Thursday, Aug. 15, 2019. A BB gun found at the teen's home is seen in the background.

FRESNO, C.A. (ABC News) – Police have arrested a 15-year-old girl in California after she allegedly posted a threat on Snapchat saying she was going to commit a shooting at her high school on Thursday.

The Fresno Police Department said it received a call from the FBI at 5 a.m. on Thursday warning them about a post on Snapchat with a photo of a gun and the message, “Don’t come to school tomorrow.” The FBI learned of the threat due to a warning from Snapchat.

“The FBI did an incredible job of tracking this information down, did a great job of really doing the leg work in this investigation,” Fresno Police Chief Jerry Dyer said at a press conference Thursday.

“During the course of the investigation we were able to determine that the actual location that the shooting was going to occur was at Edison High School.”

Using GPS, police were informed at about 6:30 a.m. that previous posts to that Snapchat account were made from a home in Fresno and officers were immediately dispatched.

When they arrived at the home, the woman who spoke to police said she was aware of the post and was the teen girl’s aunt, according to Dyer.

The girl, who attends both Edison High School and the Center for Advanced Research and Technology, a high-tech high school in Clovis, was pulled out of class by a guidance counselor and met by police.

“She, when confronted about the post, admitted to the officers that she did in fact make this threatening post, but was not able to determine, or at least convince the officers, as to why that post was made,” Dyer said.

Dyer called the post “very disturbing” and said it was of a gun display case at a Walmart store.

The unnamed minor has been charged with making a terror threat in juvenile court. She will be facing “a substantial amount of time in custody,” Dyer said.

“We take these matters very, very seriously in our community, as do law enforcement agencies and school officials across this country as a result of some of the incidents that we have seen with mass shootings,” Dyer said.

“One of the reasons we take this so seriously in law enforcement is because, No. 1, we never know when this threat will be carried out, we only know what the threat is, we don’t know whether or not the person is capable of carrying out that threat.

The other reason that we take this so seriously is because we’re very much aware of copycats.”

Dyer said the girl had a “bright future, but unfortunately she has potentially ruined her future.”

“Anything that you do on social media is immediately trackable to you, and you can’t be naive about it,” Fresno Unified School District Superintendent Bob Nelson said at the press conference. “Let me be clear, there is no joking around any issues involving school safety.”

A BB gun was found at the home of the teen, but no other guns were found, police said.

Dyer mentioned the recent mass shootings in El Paso, Texas, and Dayton, Ohio, as well as the shooting in Gilroy, California, just two hours from Fresno.

Walmart, where the Fresno teen took the photo of the rifle display case, has repeatedly defended gun sales.

The world’s largest retailer offered a defense on the same day the teen was arrested, with CEO Doug McMillon saying, “As we’ve shared previously, we will strive to use these experiences to identify additional actions we can take to strengthen our processes, improve our technology and create an even safer environment in our stores.”